Electrohydraulic brake system for motor vehicles

ABSTRACT

The present invention relates to an electro-hydraulic brake system for motor vehicles which is controllable in a ‘brake-by-wire’ operating mode by the vehicle operator as well as independently of the vehicle operator, and which can be operated in a back-up operational mode where only operation by the vehicle operator is possible. The brake system includes an emergency pressure generator or master brake cylinder which has at least one pressure chamber and is operable by means of a brake pedal, and a hydraulic auxiliary pressure source whose pressure is used to act upon wheel brakes that are connectable to the master brake cylinder by way of at least one hydraulic connection closable by means of a separating valve, as well as an electronic control and regulating unit. In order to achieve a very rapid change-over of the separating valves into the closing position, the present invention arranges for an additional electric circuit that actuates the separating valve independently of the electronic control and regulating unit as the driver&#39;s deceleration demand occurs.

TECHNICAL FIELD

[0001] The present invention generally relates to vehicle brake systemsand more particularly relates to an electro-hydraulic brake system formotor vehicles.

BACKGROUND OF THE INVENTION

[0002] An electro-hydraulic brake system of this general type is e.g.disclosed in the article ‘Das elektro-hydraulische Bremssystem vonContinental Teves—eine neue Herausforderung fur die System—undMethodenentwicklung in der Serie’ (‘The electro-hydraulic brake systemof Continental Teves—a new challenge for the series development ofsystems and methods’), VDI Berichte No. 1547, 2000. On application ofthe brake pedal, the separating valves in the prior-art brake system areswitched to assume their closed position on command of control signalsgenerated by the electronic control and regulating unit. When thecontrol or system electronics should fail, the travel simulator isblocked mechanically by one of the master cylinder pistons moving sothat the travel simulator cannot receive pressure fluid volume in theevent of actuation of the master brake cylinder in the emergency brakingmode.

[0003] The time from the commencement of actuation of the mastercylinder initiated by the driver until closing of the separating valvesis problematic in the electro-hydraulic brake system of the state of theart. When the master cylinder actuation is too quick, the mastercylinder piston blocking the travel simulator may move too far beforethe separating valves are closed. One consequence would be a ‘hard’brake pedal what could irritate the driver, and another one that only apressure sensor could still sense the extent of the deceleration demand.

BRIEF SUMMARY OF THE INVENTION

[0004] An object of the present invention is to disclose anelectro-hydraulic brake system of the type mentioned hereinabovepermitting a very rapid change-over of the separating valves into theclosed position.

[0005] This object is achieved according to the present invention byproviding an additional electric circuit, which actuates the separatingvalve independently of the electronic control and regulating unit as thedriver's deceleration demand occurs. The reaction time of the electroniccircuit is then considerably shorter than that of the electronic controland regulating unit. These measures achieve another advantage that isdirected to the condition in which the electro-hydraulic brake system isnot yet initialized (e.g. by switching on the ignition, door contact,remote control) but when the driver applies the brake pedal.

[0006] To render the idea of the present invention more specific, theelectric circuit is arranged for to have an evaluating circuit fordetecting the driver's deceleration demand that serves to enable theactuation plus the actuation of the separating valve.

[0007] According to a favorable aspect of the subject matter of thepresent invention, a timer is connected downstream of the evaluatingcircuit to generate an actuating signal for the separating valve andsuppress the actuation of the separating valve upon expiry of apredetermined duration. It is achieved by this measure that theseparating valve is disconnected after a preset time, thereby avoiding asafety-critical performance in case the system does not functionproperly.

[0008] A second safety function may be implemented in that a hardwaremonitoring circuit (watchdog) is connected downstream of the electroniccontrol and regulating unit, said monitoring circuit suppressing theactuation of the separating valve in the event of a dynamic statussignal produced by the electronic control and regulating unit differingfrom a status signal produced by the hardware monitoring circuit(watchdog).

[0009] In this arrangement, the above-mentioned actuation of theseparating valve is effected by means of two actuation logic circuitsbeing associated with a safety switch and a separating valve driverconnected in series with the separating valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a simplified circuit diagram of an electro-hydraulicbrake system of the invention.

[0011]FIG. 2 is a simplified circuit diagram of the electric circuit ofthe present invention for actuating the separating valves.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The electro-hydraulic brake system illustrated in FIG. 1comprises a dual-circuit master brake cylinder or, respectively, tandemmaster cylinder 2 that is operable by means of an actuating pedal 1 andcooperates with a pedal travel simulator 3, said master cylindercomprising two pressure chambers separated by means of two mastercylinder pistons and being in connection with an unpressurized pressurefluid supply reservoir 4. A connection between the travel simulator 3and the pressure fluid supply reservoir 4 is shut off by means of avalve device (not shown) as the second master cylinder piston (notreferred to) is moving.

[0013] Wheel brakes 7, 8 e.g. associated with the front axle areconnected to the first pressure chamber (primary pressure chamber) bymeans of a closable first hydraulic line 5. Line 5 is shut off by meansof a first separating valve 11, while an electromagnetically operable,preferably normally open (NO) pressure-compensating valve 13 is insertedinto a line portion 12 connected between the wheel brakes 7, 8, saidvalve permitting a braking pressure control on each individual wheel, ifrequired.

[0014] The second pressure chamber of the master brake cylinder 2 towhich a pressure sensor 15 may be connected is connectable with theother pair of wheel brakes 9, 10 associated with the rear axle by way ofa second hydraulic line 6 closable by means of a second separating valve14. In turn, an electromagnetically operable, preferably normally open(NO) pressure-compensating valve 19 is inserted into a line portion 16disposed between the wheel brakes 9, 10. As the design of the hydrauliccircuit connected to the second pressure chamber of the master brakecylinder 2 is identical to that one of the brake circuit 11 that isexplained in the preceding description, it need not be discussed in thefollowing text.

[0015] As can further be taken from the drawing, there is provision of amotor-and-pump assembly 20 used as an independent pressure source andincluding a high-pressure accumulator 21, said assembly being in turncomprised of a pump 23 driven by means of an electric motor 22 and apressure-limiting valve 24 connected in parallel to pump 23. The suctionside of the pump 23 is connected to the above-mentioned pressure fluidsupply reservoir 4 by way of a non-return valve 24. A pressure sensor(not shown) can monitor the hydraulic pressure generated by pump 23.

[0016] A third hydraulic line 26 connects the high-pressure accumulator21 to the inlet ports of two electromagnetic, normally closedtwo-way/two-position directional control valves 17, 18 of analogoperation which, in their capacity as inlet valves, are connectedupstream of the wheel brakes 7 and 8. Besides, the wheel brakes 7, 8 areconnected to a fourth hydraulic line 29 by way of each oneelectromagnetic, normally closed two-way/two-position directionalcontrol valve or outlet valve 27, 28 of analog operation, said line 29being in connection to the unpressurized pressure fluid supply reservoir4, on the other hand. The hydraulic pressure prevailing in the wheelbrakes 7, 8 is determined by means of each one pressure sensor 30, 31.

[0017] An electronic control and regulating unit (ECU) 32 is used tojointly actuate the motor-and-pump assembly 20 and the electromagneticvalves 11, 13, 14, 17, 18, 19, 27, 28, with the output signals of anactuating travel sensor 33 cooperating with the actuating pedal 1 and ofthe above-mentioned pressure sensor 15 being sent to the ECU as inputsignals, thereby rendering a detection of the driver's decelerationdemand possible. However, other means, for example a force sensorsensing the actuating force on the actuating pedal 1, can also be usedto detect the driver's deceleration demand. As further input quantities,the output signals of the pressure sensors 30, 31 and of wheel speedsensors (shown only schematically) are sent to the electronic controland regulating unit (ECU) 32, with reference numerals 34, 35 beingassigned to said wheel speed sensors associated with wheel brakes 7, 8.Moreover, the control and regulating unit (ECU) 32 receives signals froman additional electric circuit 36 which serves for a rapid actuation ofthe separating valves 11, 14 independently of the control and regulatingunit (ECU) 32.

[0018] The layout of the electric circuit 36 mentioned with respect toFIG. 1 becomes apparent from FIG. 2. It can be seen in the circuitdiagram illustrated therein that the signal FVW of the actuating travelsensor 33 representative of the driver's deceleration demand is sent toan evaluating circuit 40 which generates a start signal S for activatinga timer 41, an enabling signal F for a first actuating logic circuit 42and a second actuating logic circuit 43 as well as a wake signal W forthe ‘wake-up’ of the control and regulating unit (ECU) 32. The firstactuating logic circuit 42 is assigned to a safety switch 45, while thesecond actuating logic circuit 43 is used to actuate a separating valvedriver 46, with both the safety switch 45 and the separating valvedriver 46 being connected in series with the coil of the correspondingseparating valve 11, 14 being actuated. The timer 41 containing aninvariable time allowance is used to set a time limit for the activationof the actuating logic circuits 42, 43 in such a way that it produces adisabling signal S1 for deactivating the actuating logic circuits 42, 43upon expiry of the predetermined time. The electronic control andregulating unit 32 will then take care of actuating the separatingvalves 11, 14.

[0019] Should the timer 41 be defective, a second safety function isnecessary which deactivates the separating valves 11, 14 again in thecase of a faulty function of the system. A second or rather redundanttimer may e.g. safeguard the second safety function. Another solutionresides in using a hardware monitoring circuit (watchdog) 44 connecteddownstream of the control and regulating unit (ECU) 32. A dynamic statussignal WD generated by the control and regulating unit (ECU) 32 is sentto the hardware monitoring circuit (watchdog) 44, said signal containingdata about the status of the control and regulating unit (ECU) 32 andbeing compared in terms of time and value in the hardware monitoringcircuit (watchdog) 44 with the internally produced status signal. If thementioned status signals do not correlate, the hardware monitoringcircuit (watchdog) 44 will generate a second disabling signal S2 fordeactivating the actuating logic circuits 42, 43. The two disablingsignals S1, S2 are preferably sent as input signals to a pair of logicOR gates 47, 48 having output signals which disable the actuating logiccircuits 42, 43.

[0020] According to the embodiment described hereinabove, the separatingvalves 11, 14 of the two hydraulic circuits are actuated by way of theactuating circuit for defined reasons. It would principally besufficient to actuate only the separating valve 14 leading from thesecondary pressure chamber to the wheel brakes 9, 10.

1. Electro-hydraulic brake system for motor vehicles which iscontrollable in a ‘brake-by-wire’ operating mode by the vehicle operatoras well as independently of the vehicle operator, and which can beoperated in a back-up operational mode where only operation by thevehicle operator is possible, including a device for detecting thedriver's deceleration demand, an emergency pressure generator or,respectively, master brake cylinder that is operable by means of a brakepedal and has at least one pressure chamber, a travel simulator thatcooperates with the master brake cylinder and can be disconnected byactuation of the master brake cylinder, a hydraulic auxiliary pressuresource whose pressure is used to act upon wheel brakes that areconnectable to the master brake cylinder by way of at least onehydraulic connection closable by means of a separating valve, as well asan electronic control and regulating unit, characterized in that anadditional electric circuit (36) is provided which actuates theseparating valve (11, 14) independently of the electronic control andregulating unit (32) as the driver's deceleration demand occurs. 2.Electro-hydraulic brake system as claimed in claim 1, characterized inthat the reaction time of the electric circuit (36) is considerablyshorter than that of the electronic control and regulating unit (32). 3.Electro-hydraulic brake system as claimed in claim 1 or 2, characterizedin that the electric circuit (36) includes an evaluating circuit (40)for detecting the driver's deceleration demand (DDD) that serves toenable the actuation of the separating valve (11, 14). 4.Electro-hydraulic brake system as claimed in claim 3, characterized inthat connected downstream of the evaluating circuit (40) is a timer (41)that disables the actuation of the separating valve (11, 14) upon expiryof a predetermined duration.
 5. Electro-hydraulic brake system asclaimed in claim 3 or 4, characterized in that a hardware monitoringcircuit (watchdog 44) is connected downstream of the electronic controland regulating unit (32), said monitoring circuit disabling theactuation of the separating valve (11, 14) in the event of a dynamicstatus signal (WD) produced by the electronic control and regulatingunit (44) differing from a status signal produced by the hardwaremonitoring circuit (watchdog 44).
 6. Electro-hydraulic brake system asclaimed in any one of claims 1 to 5, characterized in that the actuationof the separating valve (11, 14) is effected by means of two actuationlogic circuits (42, 43) being associated with a safety switch (45) and aseparating valve driver (46) connected in series with the separatingvalve (11, 14).